---------------------------------------------------------- RotaxEngines-List Digest Archive --- Total Messages Posted Mon 04/08/13: 9 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 01:17 AM - Re: Re: Fuel return line (David Joyce) 2. 01:51 AM - Re: Fuel return line (Alan Carter) 3. 07:29 AM - Re: Re: Fuel return line (GRAHAM SINGLETON) 4. 10:36 AM - Re: Re: Fuel return line (Kevin Klinefelter) 5. 11:04 AM - Re: Re: Fuel return line (Sacha) 6. 11:36 AM - Re: Re: Fuel return line (FLYaDIVE) 7. 12:48 PM - Re: Fuel return line (Alan Carter) 8. 01:52 PM - Re: Re: Fuel return line (GRAHAM SINGLETON) 9. 05:14 PM - Re: Fuel return line (Roger Lee) ________________________________ Message 1 _____________________________________ Time: 01:17:51 AM PST US From: "David Joyce" Subject: Re: RotaxEngines-List: Re: Fuel return line Bob, I strongly suspect that altitude is of no great consequence, certainly compared with fuel temperature issues. With my 914 I have flown round the upper regions of the Alps on Mogas with no problem , and it is striking that all Austrian Rotax planes seem to use the Mogas which is available on virtually every Austrian airfield, (and I think I have been told that their CAA does not impose a height limit). The few instances of what I have diagnosed as vapour lock, that I have experienced have all been at low level in hot weather shortly after take off after stopping for lunch, when the plane has been sitting out in the sun, and under cowl temps have been very high. Regards, David Joyce, G-XSDJ On Mon, 8 Apr 2013 07:31:53 +0100 "Bob Harrison" wrote: > > > Hi! Alan/all > The Jabiru incident to which I refer was with their >engine mounted fuel pump > plus another electrical pick up pump. > But of course in my ultimate bad dream, actually a >nightmare! The Jabiru > 3300 I had fitted was never without overheating problems >...... then take it > up on Mogas in a stinking hot summer day to about >5,000ft and it lets you > know the limits of using Mogas. With the 914 Rotax I >would never fly hot and > high with Mogas, I think the recommended limits are >about 2,000ft and 20deg > C Ambient but having said that someone more clever than >me will likely > correct me ! > But the 914 on 100ll and two electrical pumps took me >safely to 17,500ft > over Mont Blanc with Ivor Phillips as a "two ship" last >August. Outside > ambient at that height was approx 4deg C but at -2deg\C >per 1000ft the > ambient at ground was very hot. (as an aside had the >Jabiru been the > "donkey" it used to struggle at less than 50ft per >minute climb at 13,000ft > like "watching paint dry" even without vaporisation !) > Sorry about that > chaps I couldn't refrain any longer ! > Bob Harrison. G-PTAG > > -----Original Message----- >From: owner-rotaxengines-list-server@matronics.com > [mailto:owner-rotaxengines-list-server@matronics.com] On >Behalf Of Alan > Carter > Sent: 07 April 2013 22:55 > To: rotaxengines-list@matronics.com > Subject: RotaxEngines-List: Re: Fuel return line > > --> > > Hi All. > My 914 has two fuel pumps, one pump has to run all the >time as i think the > 914 has no engine drive pump, Why? > These pumps are mounted well away from the engine in the >belly of the > fuselage, so cooling of the pumps is good, Has there >been any problems with > vapor lock on the 914, using Mogas. > Alan > > > > > > >Un/Subscription, >http://www.matronics.com/Navigator?RotaxEngines-List >Forums! >Admin. > > > ________________________________ Message 2 _____________________________________ Time: 01:51:33 AM PST US Subject: RotaxEngines-List: Re: Fuel return line From: "Alan Carter" Hi All. Wow 17500 ft over mountains, you chaps must have God on your side. The 914 totally reliant on Electricity, wants a little generator to pop out the side as a back up. My concern is Ethanol, have posted before on this subject. But could somebody sent me a private email on what's at the garage for flying in the UK and only at UK temperature. ie private e-mail only. Alan Read this topic online here: http://forums.matronics.com/viewtopic.php?p=398122#398122 ________________________________ Message 3 _____________________________________ Time: 07:29:55 AM PST US From: GRAHAM SINGLETON Subject: Re: RotaxEngines-List: Re: Fuel return line =C2-Sacha=0Aall sounds reasonable to me, I would just add that low pressu re caused by suction from the pump(s) could cause vaporization too. =0AI on ce had low fuel pressure because there was a minute leak upstream of the el ectric pump and at low tank contents it=0Asucked air in.=0Ano end to the va riety of gotchas out there is there?=0AGraham=0A=0A=0A=0A=0A_______________ _________________=0A From: Sacha =0ATo: rotaxengines-list @matronics.com =0ASent: Sunday, 7 April 2013, 23:38=0ASubject: RE: RotaxEng ines-List: Re: Fuel return line=0A =0A=0ABarry/Graham/Roger,=0AI=99m no expert, but I=99m going to try and summarize the arguments here. =C2- There is no question that Vapour Lock does occur and that it can be a serious problem.=C2- I plan to fly in a hot climate with mountainous te rrain (i.e. at altitude), hence my concern.=0ATo summarize what I=99m hearing:=0A-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- High fuel tem p is bad because is causes fuel to vaporize easily (so don=99t shut d own your engine suddenly and then try to restart it without cooling it as t he fuel lines will likely be heat soaked)=0A-=C2-=C2-=C2-=C2-=C2- =C2-=C2-=C2- High fuel pressure is good to the extent that =0Ao=C2- a) it increases the temp at which fuel vaporizes (though IMO this effect w ould be marginal as the Vaporization Temp varies as 1/log Pressure) and =0A o=C2- b) if a fuel return line is fitted, the fuel pump mixes the warmer fuel in the lines under the cowling with cooler fuel from the fuel tanks/ga scolator (unless you left your plane out in the sun and your wings are pain ted in a dark colour in which case fuel in your=C2- tanks might be quite warm?).=0A-=C2-=C2-=C2-=C2-=C2-=C2-=C2-=C2- Very high fuel pressure is bad because it can cause the carbs to flood, hence the advisabi lity of fitting a fuel return line=0A=C2-=0AIf one encounters vapour lock during flight, what is the best way of dealing with it, assuming one has s ufficient altitude? Reduce throttle and descent at a decent airspeed to coo l the engine?=0ASacha=0A=C2-=0A=C2-=0A=C2-=0A=C2-=0AFrom:owner-rota xengines-list-server@matronics.com [mailto:owner-rotaxengines-list-server@m atronics.com] On Behalf Of GRAHAM SINGLETON=0ASent: Sunday, 07 April, 2013 22:25=0ATo: rotaxengines-list@matronics.com=0ASubject: Re: RotaxEngines-Lis t: Re: Fuel return line=0A=C2-=0AVapour lock certainly does occur. I know of several instances, one of which resulted in a written off aircraft. It happens when the=C2-=0Aengine driven fuel pump=C2-gets heated=C2-by =C2-the engine oil and then heats the fuel. Low fuel flow rate such as =C2-when=C2-taxiing or waiting for air traffic on the ground=0Acan vapo rize the fuel, especially Mogas.=C2-The fuel return =C2-Rotax recommend keeps more fuel flowing through the system which=C2-helps=C2-cool the pump and ensures cold fuel when you need it for high power.=C2-=0AMost=C2 -carburetor=C2-installations in cars have a fuel=C2-return=C2-line for the same reasons.=0AGraham=0A=0A________________________________=0A=0AF rom:FLYaDIVE =0ATo: rotaxengines-list@matronics.com =0A Sent: Sunday, 7 April 2013, 19:08=0ASubject: Re: RotaxEngines-List: Re: Fue l return line=0A=C2-=0ASacha:=0A=C2-=0AYou have some great thought prov oking questions. =C2-I hope some are provoked.=0AFire sleeves or One piec e Molded Teflon fuel lines are the way to go.=0AYou always want to do all y ou can to keep extra heat from fuel and oil lines.=0ABUT! =C2-Where did t his Old Wives Tail of Vapor Lock come from? =C2-It is a BUNCH OF BUNK!=0A The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING t o prevent Vapor Lock. =C2-Well, almost nothing - It corrects Pilot/Builde r error.=0AVapor Lock happens ON THE GROUND and is=C2-experienced usually at start up and sometimes in the air,=C2-immediately=C2-during or afte r rotation.=0AVapor Lock can occur with MoGAs or AvGas.=0AIt is more of a P OOR PILOT SHUTDOWN PROCEDURE that anything else.=0AAnd since we are talking Home Built Planes and=C2-Self Proclaimed=C2-Engineers - - Builder erro r.=0ASo, what does the "T" fitting do? =C2-Well, the history goes way bac k to the 1960's... =C2-Electric home made Fuel Pumps were being used on =C2-Carbureted=C2-engines. And the engines were FLOODING like crazy. =C2-Flooding, Fires, Poor=C2-Starts (if at all), =C2-Dying=C2-when the throttle was floored and Low HP. =C2-All because of TOO MUCH Fuel Pre ssure Pushing the=C2-Carburetor's=C2-intake valve off the seat and floo ding the carb.=C2-=0ASo, how do you get more fuel to the carb so it does not go LEAN? =C2-You do a whole lot of pressure testing and engineering =C2-- BUT! =C2-These were HOME MADE FUEL PUMPS - And Manufacturer made Carbs. =C2-Transducers=C2-were not around then. =C2-It was too costly to try to figure out how many GPH and How much Fuel Pressure would work,an d what size spring to use... =C2-Too many variables.=0AThe QUICK and EASY and VERY=C2-Effective=C2-solution... =C2-Put a "T" fitting in the li ne and the excess pressure and excess fuel is returned to the fuel tank.=0A The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no=C2-matter=C2-how fast you hit the throttle.=0ANo Smoke and Mirr ors, No=C2-ridiculous Vapor Lock=C2-theories. =C2-But, hell, this is aviation so everybody just re-invents the wheel with their own ideas. =C2 -=0A=C2-=0AI=0A=C2-=0A=C2-=0Ahttp://www.matronics.com/Navigator?Rot axEngines-List=0Ahttp://forums.matronics.com=0Ahttp://www.matronics.com/con =========================0A ======================= ________________________________ Message 4 _____________________________________ Time: 10:36:30 AM PST US From: Kevin Klinefelter Subject: Re: RotaxEngines-List: Re: Fuel return line I operate the 914/Airmaster powered Europa regularly from high desert and cruise at 17500' over the mountains of the western US burning 91 auto gas ( up to 10% ethanol) with no problems. Kevin On Apr 8, 2013, at 1:16 AM, "David Joyce" wrote: > > > Bob, I strongly suspect that altitude is of no great consequence, certainly compared with fuel temperature issues. With my 914 I have flown round the upper regions of the Alps on Mogas with no problem , and it is striking that all Austrian Rotax planes seem to use the Mogas which is available on virtually every Austrian airfield, (and I think I have been told that their CAA does not impose a height limit). The few instances of what I have diagnosed as vapour lock, that I have experienced have all been at low level in hot weather shortly after take off after stopping for lunch, when the plane has been sitting out in the sun, and under cowl temps have been very high. > Regards, David Joyce, G-XSDJ > > On Mon, 8 Apr 2013 07:31:53 +0100 > "Bob Harrison" wrote: >> Hi! Alan/all >> The Jabiru incident to which I refer was with their engine mounted fuel pump >> plus another electrical pick up pump. >> But of course in my ultimate bad dream, actually a nightmare! The Jabiru >> 3300 I had fitted was never without overheating problems ...... then take it >> up on Mogas in a stinking hot summer day to about 5,000ft and it lets you >> know the limits of using Mogas. With the 914 Rotax I would never fly hot and >> high with Mogas, I think the recommended limits are about 2,000ft and 20deg >> C Ambient but having said that someone more clever than me will likely >> correct me ! >> But the 914 on 100ll and two electrical pumps took me safely to 17,500ft >> over Mont Blanc with Ivor Phillips as a "two ship" last August. Outside >> ambient at that height was approx 4deg C but at -2deg\C per 1000ft the >> ambient at ground was very hot. (as an aside had the Jabiru been the >> "donkey" it used to struggle at less than 50ft per minute climb at 13,000ft >> like "watching paint dry" even without vaporisation !) Sorry about that >> chaps I couldn't refrain any longer ! Bob Harrison. G-PTAG >> -----Original Message----- >> From: owner-rotaxengines-list-server@matronics.com >> [mailto:owner-rotaxengines-list-server@matronics.com] On Behalf Of Alan >> Carter >> Sent: 07 April 2013 22:55 >> To: rotaxengines-list@matronics.com >> Subject: RotaxEngines-List: Re: Fuel return line >> Hi All. >> My 914 has two fuel pumps, one pump has to run all the time as i think the >> 914 has no engine drive pump, Why? >> These pumps are mounted well away from the engine in the belly of the >> fuselage, so cooling of the pumps is good, Has there been any problems with >> vapor lock on the 914, using Mogas. >> Alan >> Un/Subscription, >> http://www.matronics.com/Navigator?RotaxEngines-List >> Forums! >> Admin. > > > > ________________________________ Message 5 _____________________________________ Time: 11:04:26 AM PST US From: "Sacha" Subject: RE: RotaxEngines-List: Re: Fuel return line Graham, Interesting, I hadn=99t thought of that one :) Another question (tell me if this is boring you): has anyone had experience of vapour lock and then been able to successfully restart the engine in flight? What steps were taken? Sacha From: owner-rotaxengines-list-server@matronics.com [mailto:owner-rotaxengines-list-server@matronics.com] On Behalf Of GRAHAM SINGLETON Sent: Monday, 08 April, 2013 15:29 Subject: Re: RotaxEngines-List: Re: Fuel return line Sacha all sounds reasonable to me, I would just add that low pressure caused by suction from the pump(s) could cause vaporization too. I once had low fuel pressure because there was a minute leak upstream of the electric pump and at low tank contents it sucked air in. no end to the variety of gotchas out there is there? Graham ________________________________ Message 6 _____________________________________ Time: 11:36:46 AM PST US Subject: Re: RotaxEngines-List: Re: Fuel return line From: FLYaDIVE Graham: You have identified yourself as a creator of myths and a woman of Old Wife's Tales. Let's take each of your statements: " I know of several instances, one of which resulted in a written off aircraft. It happens when the engine driven fuel pump gets heated by the engine oil and then heats the fuel." I'm sure there was more to it, but... That sure sounds like poor design/construction. ALL Lycoming and Continental engines have a mechanical fuel pump mounted directly to the engine case; why don't they have this mythical Vapor Lock ever warm day? YES - ALL engines take the chance of Vapor Lock, but, it is things like aluminum fuel lines, TEFLON fuel lines and Fire Sleeves that prevent it. And more so proper handling by the pilot/builder. I have flown 5 planes on MoGas over a 12 year period and NEVER had Vapor Lock. Yes, in the summer's of the Mid Atlantic I also caused Vapor Lock in a C-172 using AvGas, just to prove it can be done. Of course on the ground and it was done after an improper shutdown and inproper restart. Vapor Lock - CANNOT be created when there is fuel flow. As long as the fuel is flowing it is not expanding. It MUST happen at shut down. UNLESS - as I said some very poor building practices were followed, which ran a fuel line next to or above a hot point such as an exhaust pipe. I'm trying to believe that even if the builder made that mistake the DAR would have caught it. AND isn't this the supposed purpose of installing the "T" fitting. Vapor Lock requires two things: 1 - The fuel to be heated allowing it to expand and 2 - A place for the expanded gas (VAPOR) to be TRAPPED. Such a Up or Down U bend or a pig-tail. End of your first myth . Second myth: "The fuel return Rotax recommend keeps more fuel flowing through the system which helps cool the pump and ensures cold fuel when you need it for high power." Where to begin with this one, it is equivalent to cleaning the Augean Stables. Part A: If you have two pumps in series Pump X and Pump Y. And Pump X comes from the tank and Pump Y feeds into the carb. And Pump X feeds at 10 PSI and 10 GPH and Pump Y Pushes at 12 PSI and 12 GPH what do you think will happen in the connection between the two pumps? Since Pump Y requires/displaces more fuel than Pump X can deliver there will be a LOSS of fuel between the two... To the untrained eye that may look like a Vapor Lock but it is just Fuel Starvation. That is why you place the HIGHER supplying pump (Pump X) before the lower supplying pump (Pump Y). You can always reduce what you have - You can't reduce what you don't have. Part B: If there you have fuel at Zero Deg F and it is not flowing through the pump there is NO cooling taking place. Sure there is some conduction BUT the mass of the fuel pump Vs the mass of the fuel in the fuel line and the line itself is NOT worth considering. Ah, but I just did, just in case you use Machiavellian Logic. What kind of fuel lines are people using? Part C: Let's use some of this ridiculous logic that is being spewed forth... Let's say you have a really terrible cooling system on your plane and through the use of this Magic "T" fitting the Hot fuel is being returned to the tank. What about the fuel that is in the line between the electric fuel pump and the mechanical fuel pump of the HOT engine? Why isn't that causing Vapor Lock? Then again it may? All dependent on how well the builder did their job. Questions: How many are using TYGON fuel lines? How many are using some-other plastic fuel line? Third myth: "Most carburetor installations in cars have a fuel return line for the same reasons." Most old carbureted cars NEVER had a fuel return line. As I stated before, when electric fuel pumps came into play they needed a method of increasing fuel flow without flooding the carb, therefore "T" fittings and fuel return lines. Fuel return lines came into play NOT because of Vapor Lock but because of: a> The EPA - They did not want gas fumes evaporating into the atmosphere. b> This was first fought by the car manufactures but later was proven to be helpful BECAUSE they were able to brag (advertise) about an INCREASE in gas mileage... Not really true - But just that you had more gas in you tank due to less evaporation. How much more? Ask the EPA! Today all cars have return lines and pressure gas caps and many have fuel injection. So if one wants to use Machiavellian Logic here again - - - It was because of Vapor Lock. NOT! A Vapor Lock is the Void between a myth being trapped in the mind and the truth trying to replace it. Barry Hey, I'm 7 days late but: Did you know you have to do a New W&B if you change from AvGas to MoGas because MoGas does not have Lead! On Sun, Apr 7, 2013 at 5:25 PM, GRAHAM SINGLETON < grahamsingleton@btinternet.com> wrote: > Vapour lock certainly does occur. I know of several instances, one of > which resulted in a written off aircraft. It happens when the engine > driven fuel pump gets heated by the engine oil and then heats the fuel. Low > fuel flow rate such as when taxiing or waiting for air traffic on the > ground can vaporize the fuel, especially Mogas. The fuel return Rotax > recommend keeps more fuel flowing through the system which helps cool the > pump and ensures cold fuel when you need it for high power. > Most carburetor installations in cars have a fuel return line for the same > reasons. > Graham > ------------------------------ > *From:* FLYaDIVE > *To:* rotaxengines-list@matronics.com > *Sent:* Sunday, 7 April 2013, 19:08 > *Subject:* Re: RotaxEngines-List: Re: Fuel return line > > Sacha: > > You have some great thought provoking questions. I hope some are provoked. > Fire sleeves or One piece Molded Teflon fuel lines are the way to go. > You always want to do all you can to keep extra heat from fuel and oil > lines. > BUT! Where did this Old Wives Tail of Vapor Lock come from? It is a > BUNCH OF BUNK! > The "T" fitting does NOTHING for Vapor Lock... High Pressure does NOTHING > to prevent Vapor Lock. Well, almost nothing - It corrects Pilot/Builder > error. > Vapor Lock happens ON THE GROUND and is experienced usually at start up > and sometimes in the air, immediately during or after rotation. > Vapor Lock can occur with MoGAs or AvGas. > It is more of a POOR PILOT SHUTDOWN PROCEDURE that anything else. > And since we are talking Home Built Planes and Self Proclaimed Engineers - > - Builder error. > So, what does the "T" fitting do? Well, the history goes way back to the > 1960's... Electric home made Fuel Pumps were being used > on Carbureted engines. And the engines were FLOODING like crazy. Flooding, > Fires, Poor Starts (if at all), Dying when the throttle was floored and > Low HP. All because of TOO MUCH Fuel Pressure Pushing > the Carburetor's intake valve off the seat and flooding the carb. > So, how do you get more fuel to the carb so it does not go LEAN? You do a > whole lot of pressure testing and engineering - BUT! These were HOME MADE > FUEL PUMPS - And Manufacturer made Carbs. Transducers were not around > then. It was too costly to try to figure out how many GPH and How much > Fuel Pressure would work,and what size spring to use... Too many variables. > The QUICK and EASY and VERY Effective solution... Put a "T" fitting in > the line and the excess pressure and excess fuel is returned to the fuel > tank. > The Carb takes what it needs - Has a steady supply of fuel and does NOT go > lean no matter how fast you hit the throttle. > No Smoke and Mirrors, No ridiculous Vapor Lock theories. But, hell, this > is aviation so everybody just re-invents the wheel with their own ideas. > > I > > ** > > ________________________________ Message 7 _____________________________________ Time: 12:48:09 PM PST US Subject: RotaxEngines-List: Re: Fuel return line From: "Alan Carter" Hello All. I like the idea that a vapor lock will not occur when the fuel is flowing, this make scene to me, but will occur on the ground with a hot engine. The fuel has got to turn to vapor and expand along the fuel pipe so locking it, and i would not think this would happen in a flowing fuel line. Engines stop in flight from fuel starvation, but this could be for many reasons, and if unknown, claimed a vapour lock. But im not convinced, Kevin, your another high flyer , do you use a oxygen mask up at 17.5 Alan Read this topic online here: http://forums.matronics.com/viewtopic.php?p=398172#398172 ________________________________ Message 8 _____________________________________ Time: 01:52:56 PM PST US From: GRAHAM SINGLETON Subject: Re: RotaxEngines-List: Re: Fuel return line "Vapour lock" not a good name perhaps occurs when the fuel boils and vapour flows into the carburetor.=0AThen the mixture is all wrong and the engine won't give power.=0AIt tends to occur when fuel flow is very low so the fue l doesn't cool the Rotax pump. Taxying with a hot engine on a hot day=0Athe n trying to take off.=0ABit of thinking required imho=0AGraham=0A=0A=0A=0A =0A________________________________=0A From: FLYaDIVE =0ATo: rotaxengines-list@matronics.com =0ASent: Monday, 8 April 2013, 19:36 =0ASubject: Re: RotaxEngines-List: Re: Fuel return line=0A =0A=0AGraham:=0A =0AYou have identified yourself as a creator of myths and a woman of Old Wi fe's-Tales.--Let's take each of your-statements:=0A=0AVapor Lock - CANNOT be created when there is fuel flow. -As long as the fuel is flowin g it is not expanding. -It MUST happen at shut down. -UNLESS - as I sai d some very poor building-practices were followed, which ran a fuel line next to or above a hot point such as an exhaust pipe. -I'm trying to-be lieve-that even if the builder made that mistake the DAR would have caugh t it. -AND isn't this the supposed purpose of installing the "T" fitting. -=0AVapor Lock requires two things:=0A1 - The fuel to be heated allowing it to expand and=0A2 - A place for the expanded gas (VAPOR) to be TRAPPED. =0ASuch a Up or Down U bend or a pig-tail. -=0AEnd of your first myth . =0A=0ASecond myth: "The fuel return Rotax recommend keeps more fuel flowing through the system which-helps-cool the pump and ensures cold fuel whe n you need it for high power." -Where to begin with this one, it is-equ ivalent-to cleaning the Augean Stables.=0APart A: -If you have two pump s in series Pump X and Pump Y. -And Pump X comes from the tank and Pump Y feeds into the carb. -And Pump X feeds at 10 PSI and 10 GPH and Pump Y P ushes at 12 PSI and 12 GPH what do you think will happen in the connection between the two pumps? -=0ASince Pump Y requires/displaces more fuel than Pump X can deliver there will be a LOSS of fuel between the two... -To t he untrained eye that may look like a Vapor Lock but it is just Fuel Starva tion. -That is why you place the HIGHER supplying pump (Pump X) before th e lower-supplying-pump (Pump Y). -You can always reduce what you have - You can't reduce what you don't have.=0APart B: -If there you have fue l at Zero Deg F and it is not flowing through the pump there is NO cooling taking place. -Sure there is some conduction BUT the mass of the fuel pum p Vs the mass of the fuel in the fuel line and the line itself is NOT worth considering. -Ah, but I just did, just in case you use-Machiavellian -Logic. - What kind of fuel lines are people using?=0APart C: -Let's use some of this-ridiculous-logic that is being-spewed-forth... - Let's say you have a really-terrible-cooling system on your plane and t hrough the use of this Magic "T" fitting the Hot fuel is being returned to the tank. -What about the fuel that is in the line between the electric f uel pump and the mechanical fuel pump of the HOT engine? Why isn't that cau sing Vapor Lock? -Then again it may? -All dependent on how well the bui lder did their job. -=0A=0AQuestions: -How many are using TYGON fuel li nes? -How many are using-some-other-plastic fuel line?=0A=0AThird myt h: "Most-carburetor-installations in cars have a fuel-return-line f or the same reasons." -Most old-carbureted-cars NEVER had a fuel retu rn line. -As I stated before, when electric fuel pumps came into play the y needed a method of increasing fuel flow without flooding the carb, theref ore "T" fittings and fuel return lines. -Fuel return lines came into play NOT because of Vapor Lock but because of:=0Aa> The EPA - They did not want gas fumes-evaporating-into the-atmosphere.=0Ab> This was first-fou ght-by the car manufactures but later was proven to be helpful BECAUSE th ey were able to brag (advertise) about an INCREASE in gas-mileage... Not really true - But just that you had more gas in you tank due to less evapor ation. -How much more? -Ask the EPA!=0AToday all cars have return lines and pressure gas caps and many have fuel injection. -So if one wants to use-Machiavellian-Logic here again - - - It was because of Vapor Lock. -NOT!=0A=0AA Vapor Lock is the Void between a myth being trapped in the m ind and the truth trying to replace it.=0A=0ABarry=0A=0AHey, I'm 7 days lat e but: -Did you know you have to do a New W&B if you change from AvGas to MoGas because MoGas does not have Lead!=0A=0A=0A=0A=0AOn Sun, Apr 7, 2013 at 5:25 PM, GRAHAM SINGLETON wrote:=0A=0AV apour lock certainly does occur. I know of several instances, one of which resulted in a written off aircraft. It happens when the-engine driven fue l pump-gets heated-by-the engine oil and then heats the fuel. Low fue l flow rate such as -when-taxiing or waiting for air traffic on the gro und-can vaporize the fuel, especially Mogas.-The fuel return -Rotax r ecommend keeps more fuel flowing through the system which-helps-cool th e pump and ensures cold fuel when you need it for high power.-=0A>Most- carburetor-installations in cars have a fuel-return-line for the same reasons.=0A>Graham=0A>=0A>________________________________=0A> From: FLYaD IVE =0A>To: rotaxengines-list@matronics.com =0A>Sent: S unday, 7 April 2013, 19:08=0A>Subject: Re: RotaxEngines-List: Re: Fuel retu rn line=0A> =0A>=0A>=0A>Sacha:=0A>=0A>=0A>You have some great thought provo king questions. -I hope some are provoked.=0A>Fire sleeves or One piece M olded Teflon fuel lines are the way to go.=0A>You always want to do all you can to keep extra heat from fuel and oil lines.=0A>BUT! -Where did this Old Wives Tail of Vapor Lock come from? -It is a BUNCH OF BUNK!=0A>The "T " fitting does NOTHING for Vapor Lock... High Pressure does NOTHING to prev ent Vapor Lock. -Well, almost nothing - It corrects Pilot/Builder error. =0A>Vapor Lock happens ON THE GROUND and is-experienced usually at start up and sometimes in the air,-immediately-during or after rotation.=0A>V apor Lock can occur with MoGAs or AvGas.=0A>It is more of a POOR PILOT SHUT DOWN PROCEDURE that anything else.=0A>And since we are talking Home Built P lanes and-Self Proclaimed-Engineers - - Builder error.=0A>So, what does the "T" fitting do? -Well, the history goes way back to the 1960's... -Electric home made Fuel Pumps were being used on-Carbureted-engines. And the engines were FLOODING like crazy. -Flooding, Fires, Poor-Start s (if at all), -Dying-when the throttle was floored and Low HP. -All because of TOO MUCH Fuel Pressure Pushing the-Carburetor's-intake valve off the seat and flooding the carb.-=0A>So, how do you get more fuel to the carb so it does not go LEAN? -You do a whole lot of pressure testing and engineering -- BUT! -These were HOME MADE FUEL PUMPS - And Manufact urer made Carbs. -Transducers-were not around then. -It was too costl y to try to figure out how many GPH and How much Fuel Pressure would work,a nd what size spring to use... -Too many variables.=0A>The QUICK and EASY and VERY-Effective-solution... -Put a "T" fitting in the line and the excess pressure and excess fuel is returned to the fuel tank.=0A>The Carb takes what it needs - Has a steady supply of fuel and does NOT go lean no -matter-how fast you hit the throttle.=0A>No Smoke and Mirrors, No-ri diculous Vapor Lock-theories. -But, hell, this is aviation so everybody ============== ________________________________ Message 9 _____________________________________ Time: 05:14:06 PM PST US Subject: RotaxEngines-List: Re: Fuel return line From: "Roger Lee" Hi Barry, I think you are only partially right and missed several qualifiers and exacerbating contributory issues. They talk about vapor lock in flight, but I have not personally seen it happen, but there are a thousand different planes designs out there and Rotax didn't just pull this out of a hat. It probably happened somewhere. Here are some of the problems. It isn't just fuel flow, it must have a sufficient quantity flowing so the heat doesn't have time to heat the fuel up to vaporize. Having exposed fuel lines without fire sleeve not only leaves the fire danger on the table, but allows for more heat to the fuel. The Rotax or a small size engine may not flow enough fuel and if the engine is encased in a cowl and has a lack of or poor air flow and the fuel flow gets reduced and the fuel sets long enough in the fuel line vapor can happen and the fuel will be flowing. Vapor lock can happen when an engine is running with fuel flow. My Dad's old Packard used to get vapor lock especially going up into the mountains at a slow pace and getting hotter than normal or an engine with a reduced cooling air flow. It isn't just whether fuel is flowing it depends on the quantity that flows. If the quantity is very small, but still flowing and in an excessively hot area it can absolutely vapor lock, just like the old cars. Fuel flow quantity is the key and the enclosed environment plus heat becomes the next problem. I usually don't see vapor lock while flying and most never will, but I absolutely see it all the time after a plane has landed and sat for 30+ minutes. Then on start up the fuel pressure is 1-1.5 psi until the cooler fuel flows into the upper fuel lines. In a tightly cowed engine the heat is higher with no fuel flow right after shut down. That said I haven't seen an engine cough because of it yet. Putting just a Tee in is really not a re-circulation line. It must have a restrictor in place otherwise you wouldn't have any fuel pressure. Vapor lock seems to happen more on the ground and things aren't cooling as well and there is less fuel flow. A "U" shape fitting won't guarantee or eliminate vapor lock. As the fuel sits in the hot environment more vapor can form and as it expands it will over come the "U" fitting area and expand into the hoses. It all depends on the heat amount, the fuel line surface area, insulating factors( i.e. fire sleeve), air flow for cooling and fuel flow quantity. After sitting on the ground and starting up with vapor in the lines, then usually a taxi out to a runway will take care of the issue. -------- Roger Lee Tucson, Az. Light Sport Repairman - Maintenance Rated Rotax Repair Center - Heavy Maint. 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